1. Technical Field
This invention relates generally to a system for measuring the composition, velocity and volumetric flow rate of each phase of a multi-phase mixture (e.g., oil, water, and gas mixture) having entrained gas therein, and more particularly to a system that measures the speed of sound propagating through a flow to determine compositional measurements compensated for entrained gas.
2. Background Information
Currently, there is an unmet need for multiphase flow measurement in oil and gas production. In fact, the accurate monitoring of well head production rates in the presence of entrained gas has long presented a difficult technical challenge to the oil and gas industry. Performing accurate and timely monitoring of the production rates has many benefits, including the optimization of overall field production and specific well production. The difficulty is due in no small part to the extreme variability of produced fluids which can include various types and mixtures of oil, water, gas, and solid particles.
In response to the above discussed issues, many companies have developed various types of three phase meters that are designed to address the well head flow metering market. However, these products have met relatively limited commercial success due to a combination of performance, accuracy, and cost issues. In light of this, the present invention provides a means and apparatus for well head monitoring that combines multiple existing technologies to meet a wide range of cost and performance goals.
Another difficulty with measuring the composition of the oil/water mixture at the well head involves the pipe not being continuously filled during the pumping processes. In other words, the gas void fraction may randomly vary from 0% to 50%. Unfortunately, current apparatus for measuring the gas void fraction has difficulty or may not be able to accurately measure the gas void fraction of the oil and gas mixture. The present invention provides a continuous real-time measurement of the oil and water mixture having entrained air that temporally varies as the mixture flows through the pipe.
“Slugging” is a common phenomenon in the transport of gas/liquid mixtures, wherein liquid component bodies (i.e., “slugs”) are dispersed within a gas/liquid flow. A slug is present within a pipe at a given location when the liquid component body fills substantially all of the cross-sectional area of the pipe at the location. The slug may consist of a single component (i.e., water or liquid hydrocarbon) or a mixture of components (e.g., a mixture of water and liquid hydrocarbon). A slug may include some amount of entrained gases, which entrained gases are distinguishable from gas component bodies within the flow by virtue of the amount of gas present. A liquid slug and a gas component body cannot both be present at a particular location in the pipe at the same time. Naturally occurring slugs vary in length, speed, duration and quality. The transient nature of the presence of slugs, and therefore the transient nature of the liquid continuous conditions, makes it desirable to identify the fluid sound speed as quickly and accurately as possible.
The dynamics of gas/liquid flows can be very complicated. FIG. 15 schematically illustrates some of the more commonly occurring types of flow regimes that may be found in horizontal fluid flows. Gas/liquid flows can take many forms, however, and are therefore not limited to these illustrative flow regime examples. The term “horizontal” as used herein is defined as a direction that is substantially perpendicular to the local gravity vector.
What is needed is a system and method for determining at least one characteristic of a fluid flowing within a pipe, one that can accommodate a variety of fluid flows within a pipe, which flow may include one or more gas component bodies and one or more liquid component bodies.